Various methods have been used to determine the location of a touch on a touch sensitive panel. Touch location may be determined, for example, using a number of force sensors coupled to the touch panel. The force sensors generate an electrical signal that changes in response to a touch. The relative magnitudes of the signals generated by the force sensors may be used to determine the touch location.
Capacitive touch location techniques involve sensing a current change due to capacitive coupling created by a touch on the touch panel. A small amount of voltage is applied to a touch panel at several locations, for example, at each of the touch panel corners. A touch on the touch panel couples in a capacitance that alters the current flowing from each corner. The capacitive touch system measures the currents and determines the touch location based on the relative magnitudes of the currents.
Resistive touch panels are typically multilayer devices having a flexible top layer and a rigid bottom layer separated by spacers. A conductive material or conductive array is disposed on the opposing surfaces of the top and bottom layers. A touch flexes the top layer causing contact between the opposing conductive surfaces. The system determines the touch location based on the change in the touch panel resistance caused by the contact.
Touch location determination may rely on optical or acoustic signals. Infrared techniques used in touch panels typically utilize a specialized bezel that emits beams of infrared light along the horizontal and vertical axes. Sensors detect a touch that breaks the infrared beams.
Surface Acoustic Wave (SAW) touch location processes use high frequency waves propagating on the surface of a glass screen. Attenuation of the waves resulting from contact of a finger with the glass screen surface is used to detect touch location. SAW typically employs a “time-of-flight” technique, where the time for the disturbance to reach the pickup sensors is used to detect the touch location. Such an approach is possible when the medium behaves in a non-dispersive manner, such that the velocity of the waves does not vary significantly over the frequency range of interest.
Bending wave touch technology senses vibrations created by a touch in the bulk material of the touch sensitive substrate. These vibrations are denoted bending waves and may be detected using bending mode sensors typically placed on the edges of the substrate. Signals generated by the sensors are analyzed to determine the touch location. In some implementations, the sensor signals may be processed to account for frequency dispersion caused by the substrate material.
For any of the technologies outlined above, increasing the accuracy and/or speed of touch location determination and decreasing the processing and/or cost of the implementation is desirable. The present invention fulfils these and other needs, and offers other advantages over the prior art.